U.S. patent application number 15/304263 was filed with the patent office on 2017-02-09 for tunable emitting device with a directly modulated laser coupled to a ring resonator.
The applicant listed for this patent is ALCATEL LUCENT. Invention is credited to Nicolas CHIMOT, Siddharth JOSHI, Francois LEARGE.
Application Number | 20170040773 15/304263 |
Document ID | / |
Family ID | 50630729 |
Filed Date | 2017-02-09 |
United States Patent
Application |
20170040773 |
Kind Code |
A1 |
CHIMOT; Nicolas ; et
al. |
February 9, 2017 |
TUNABLE EMITTING DEVICE WITH A DIRECTLY MODULATED LASER COUPLED TO
A RING RESONATOR
Abstract
An emitting device (1) is intended for delivering photons with a
chosen wavelength. This emitting device (1) comprises an InP
substrate (2) with a directly modulated laser (3) arranged for
generating photons modulated by a non-return-to-zero modulation to
produce data to be transmitted, a passive ring resonator (4)
monolithically integrated with the directly modulated laser (3) and
having a resonance amongst several ones that is used for filtering
a zero level induced by the data modulation, and a tuning means (5)
arranged along the directly modulated laser (3) and/or around the
ring resonator (4) to tune the photon wavelength and/or the ring
resonator resonance used for filtering.
Inventors: |
CHIMOT; Nicolas;
(Marcoussis, FR) ; LEARGE; Francois; (Marcoussis,
FR) ; JOSHI; Siddharth; (Marcoussis, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ALCATEL LUCENT |
Boulogne-Billancourt |
|
FR |
|
|
Family ID: |
50630729 |
Appl. No.: |
15/304263 |
Filed: |
April 15, 2015 |
PCT Filed: |
April 15, 2015 |
PCT NO: |
PCT/EP2015/058142 |
371 Date: |
October 14, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01S 5/223 20130101;
H01S 5/06251 20130101; H01S 5/0612 20130101; H01S 5/34 20130101;
H01S 5/1071 20130101; H01S 5/12 20130101; H01S 5/026 20130101; H01S
5/1025 20130101; H01S 5/005 20130101; H01S 5/3054 20130101; H01S
5/06255 20130101; H01S 5/1032 20130101 |
International
Class: |
H01S 5/10 20060101
H01S005/10; H01S 5/12 20060101 H01S005/12; H01S 5/223 20060101
H01S005/223; H01S 5/34 20060101 H01S005/34; H01S 5/30 20060101
H01S005/30; H01S 5/06 20060101 H01S005/06 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 16, 2014 |
EP |
143005568.9 |
Claims
1. Emitting device for delivering photons with a chosen wavelength,
said emitting device comprising: i) an InP substrate with a
directly modulated laser arranged for generating photons modulated
by a non-return-to-zero modulation to produce data to be
transmitted, the active structure of the directly modulated laser
being epitaxially grown on the InP substrate, ii) a passive ring
resonator being defined in a passive section of the InP substrate,
said passive ring resonator being monolithically integrated with
said directly modulated laser by carrying out a p-doped re-growth
both in the active and passive sections of the InP substrate
followed by a hydrogenation of the passive section of the InP
substrate for rendering the p-doping of the re-growth inactive,
said passive ring resonator having a resonance amongst several ones
that is used for filtering a zero level induced by said data
modulation, and iii) a tuning means arranged along said directly
modulated laser and/or around said ring resonator to tune the
photon wavelength and/or said ring resonator resonance used for
filtering.
2. Emitting device according to claim 1, wherein said ring
resonator is butt-joined to said directly modulated laser to reduce
insertion losses.
3. Emitting device according to one of claim 1, wherein said tuning
means comprises heating electrodes arranged along said directly
modulated laser and/or around said ring resonator and defining a
Peltier heater.
4. Emitting device according to one of claim 1, wherein said tuning
means comprises a controlled phase-shift section defined into said
directly modulated laser.
5. Emitting device according to one of claim 1, wherein said
directly modulated laser is made of multi-quantum wells or quantum
dashes active layers combined with an optimized buried ridge stripe
technology.
6. Emitting device according to claim 5, wherein said directly
modulated laser has an adiabatic chirp comprised between
approximately 1 GHz and 8 GHz.
7. Emitting device according to claim 1, wherein it further
comprises a first semiconducting optical amplifier defined inside
said ring resonator to modify optical losses and arranged for
adjusting an on/off ratio characteristic and a steepness slope
characteristic to modify optical losses.
8. Emitting device according to claim 1, wherein it further
comprises a passive taper section after said ring resonator.
9. Emitting device according to claim 1, wherein it further
comprises an integrated photodiode defined upward said directly
modulated laser and arranged for monitoring optical power.
10. Emitting device according to claim 1, wherein it further
comprises a second semiconducting optical amplifier defined
downward said ring resonator and arranged for compensating optical
losses.
11. A process for producing an emitting device comprising the
following steps: performing an epitaxial growth of the active
structure of the directly modulated laser on the InP substrate,
carrying out a butt-joint in order to allow growth of the passive
structure of a passive ring resonator, defining a Bragg array into
the active structure of the directly modulated laser in order to
define a directly modulated laser of DFB type, defining active and
passive bands, a waveguide with a ring shape being part of the
passive ring resonator and a waveguide coupling the directly
modulated laser to the passive ring resonator, said waveguide being
tangent to the passive ring resonator, carrying out a p-doped
re-growth both in the active and passive sections, defining
metallic contacts for the directly modulated laser, defining
metallic heating electrodes near the passive ring resonator,
performing a hydrogenation of the passive section for rendering the
p doping of the re-growth inactive.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to tunable emitting devices
that can be notably used in optical access networks.
BACKGROUND
[0002] As known by the man skilled in the art there is an
increasing demand for a high transmission reach in optical access
networks, typically 40 km or even 60 km, in order to get downstream
and upstream nominal line rates per channel equal to 10 Gb/s and
2.5 Gb/s or 10 Gb/s respectively.
[0003] There is also a demand for high dynamic extinction ratio (or
DER), typically 6 dB or even 8 dB.
[0004] Several solutions have been proposed to reach at least one
of the above mentioned characteristics.
[0005] A first solution consists in carrying out a proper
management of chirp and spectrum reshaping. This first solution is
rather well adapted to reach intermediate distances (typically
between 100 km and 300 km) and/or to allow reducing the spectral
broadening through dual modulation. But it induces a DER that is
too low.
[0006] A second solution consists in using an electro-absorption
modulator (or EML). But it induces a loss of optical power due to
the absorption into the modulator. To improve the situation it is
possible to use a passive taper section and to grow different
materials for the laser and the modulator. But this increases the
technology complexity and leads to a high consumption 3-sections
device.
[0007] A third solution consists in using an integrated chirp
managed laser (or CML) with an optical spectrum re-shaper to
increase dispersion tolerance, However, the targeted transmission
distance ranges (from 200 km to 600 km) are far beyond the optical
access network standards. Beside, this solution makes necessary to
precisely tune the laser wavelength to the optical spectrum
re-shaper characteristic, which requires the use of a complex
feedback loop that makes it viable for very long distance networks
but unsuitable for low cost applications.
[0008] A fourth solution consists in using a transmitter optical
sub-assembly (or TOSA) with an hybrid integration of directly
modulated lasers (or DML) and free-space-optics assembly for signal
spectral filtering. This solution fully fits to the distance
transmission and DER requirements, but its main drawback is the
complexity of the module packaging since a precise alignment of the
on-wafer laser with the free-space-optics is required, which
induces additional coupling losses that could be a limitation for a
stringent optical budget recommendation in an optical access
network. Moreover, the achieved performances are only possible by
means of a complex and power consuming electronic dispersion
compensation (or EDC) system.
[0009] A fifth solution consists in using a planar ligthwave
circuit (or PLC). This allows achieving a 300 km transmission at 10
Gb/s without any optical or electrical dispersion compensation.
However, the fabrication and use appear to be complex since two
monitor port photodiodes are requested and high insertion losses
are expected from the hybrid integration of III-V semiconductor
based laser on silicon platform.
SUMMARY
[0010] So an object of this invention is to improve the situation,
and notably to allow data transmission over at least 40 km of a
single mode fiber (or SMF) with an extinction ratio higher than 6
dB and high output power (or high optical budget).
[0011] In an embodiment, an emitting device is intended for
delivering photons with a chosen wavelength, and comprises: [0012]
an InP substrate with a directly modulated laser (or DML) arranged
for generating photons modulated by a (typical) non-return-to-zero
(or NRZ) modulation to produce data to be transmitted, the active
structure of the directly modulated laser being epitaxially grown
on the InP substrate, [0013] a passive ring resonator being defined
in a passive section of the InP substrate, said passive ring
resonator being monolithically integrated with said directly
modulated laser by carrying out a p-doped re-growth both in the
active and passive sections of the InP substrate followed by a
hydrogenation of the passive section of the InP substrate for
rendering the p-doping of the re-growth inactive, said passive ring
resonator having a resonance amongst several ones that is used for
filtering a zero level induced by the data modulation, and [0014] a
tuning means arranged along this directly modulated laser and/or
around this ring resonator to tune the photon wavelength and/or the
ring resonator resonance used for filtering.
[0015] This allows producing a simple, low cost and low consumption
device that is compatible with existing packaging solutions, such
as a transistor outline-can (or TO-can) module.
[0016] The tunable emitting device may include additional
characteristics considered separately or combined, and notably:
[0017] its ring resonator may be butt-joined to its directly
modulated laser, in order to reduce insertion losses; [0018] in a
first embodiment its tuning means may comprise heating electrodes
arranged along its directly modulated laser and/or around its ring
resonator and defining a Peltier heater; [0019] in a second
embodiment its tuning means may comprise a controlled phase-shift
section defined into its directly modulated laser; [0020] its
directly modulated laser may be made of multi-quantum wells or
quantum dashes active layers combined with an optimized buried
ridge stripe (or BRS) technology, in order to get a low electrical
bandwidth; [0021] its directly modulated laser may have an
adiabatic chirp comprised between approximately 1 GHz and 8 GHz;
[0022] it may further comprise a first semiconducting optical
amplifier (or SOA) defined inside its ring resonator to modify
optical losses and arranged for adjusting an on/off ratio
characteristic and a steepness slope characteristic to modify
optical losses. This can be done without extra technological step
since the SOA material can be the same as the one of the directly
modulated laser. The on/off ratio characteristic is the contrast
value between the maximum of transmission and the minimum down in
each resonance of the transfer function of the ring resonator;
[0023] it may further comprise a passive taper section after its
ring resonator; [0024] it may further comprise an integrated
photodiode defined upward its directly modulated laser and arranged
for monitoring optical power; [0025] it may further comprise a
second semiconducting optical amplifier defined downward its ring
resonator and arranged for compensating optical losses.
[0026] Yet another embodiment comprises a process for producing an
emitting device comprising the following steps: [0027] performing
an epitaxial growth of the active structure of the directly
modulated laser on the InP substrate, [0028] carrying out a
butt-joint in order to allow growth of the passive structure of a
passive ring resonator, [0029] defining a Bragg array into the
active structure of the directly modulated laser in order to define
a directly modulated laser of DFB type, [0030] defining active and
passive bands, a waveguide with a ring shape being part of the
passive ring resonator and a waveguide coupling the directly
modulated laser to the passive ring resonator, said waveguide being
tangent to the passive ring resonator, [0031] carrying out a
p-doped re-growth both in the active and passive sections, [0032]
defining metallic contacts for the directly modulated laser, [0033]
defining metallic heating electrodes near the passive ring
resonator, [0034] performing a hydrogenation of the passive section
for rendering the p doping of the re-growth inactive.
BRIEF DESCRIPTION OF THE FIGURES
[0035] Some embodiments of a tunable emitting device are now
described, by way of example only, and with reference to the
accompanying drawings, in which:
[0036] FIG. 1 schematically illustrates, in a top view, a first
example of embodiment of a tuning emitting device, and
[0037] FIG. 2 schematically illustrates, in a top view, a second
example of embodiment of a tuning emitting device.
DESCRIPTION OF EMBODIMENTS
[0038] Hereafter is notably disclosed a tuning emitting device 1
intended for delivering photons with a chosen wavelength.
[0039] This tuning emitting device 1 may be part of an
optoelectronic component, such as a transistor outline-can (or
TO-can) module, for instance. Generally speaking, it may be used in
optical access networks, such as Passive Optical Networks (or PONs)
and especially, but not limitatively, in next generation PONs, and
notably XG-PON1 or NG-PON ("N Gigabits-PON"), for instance.
[0040] Examples of tuning emitting devices 1 according to
embodiments of the invention are schematically illustrated in FIGS.
1 and 2. As illustrated in these non-limiting examples, a tuning
emitting device 1 comprises an InP substrate 2 with at least a
directly modulated laser (or DML) 3, a passive ring resonator 4,
and a tuning means.
[0041] The directly modulated laser (or DML) 3 is defined onto the
InP substrate 2 and arranged for generating photons modulated by a
(typical) non-return-to-zero (or NRZ) modulation to produce data to
be transmitted. So, the data modulation written on the optical
power generated by the DML 3 is made by a sequence of "one" and
"zero".
[0042] The DML 3 presents a very efficient damping of the resonance
frequency and, as a consequence, presents a low transient chirp
(typically <2 GHz). It is a major concern since transient chirp
is very detrimental for data transmission over single mode fiber
(or SMF).
[0043] In order to reduce the transient chirp, the DML 3 can be
made of multi-quantum wells (or MQWs) or quantum dashes (or Washes)
active layers combined with an optimized buried ridge stripe (or
BRS) technology, to get a low electrical bandwidth.
[0044] Preferably, the DML 3 is arranged in order to show an
adiabatic chirp comprised between approximately 1 GHz and
approximately 8 GHz, and possibly between 1 GHz and 5 GHz. This
interval of values allows to run easily the DML 3 with the ring
resonator 4. The larger the adiabatic chirp is, the lower the
resonance slope has to be in order to get a similar extinction
ratio value.
[0045] The passive ring resonator 4 is defined onto the InP
substrate 2 in a passive section, monolithically integrated with
the DML 3, and having a resonance amongst several ones that is used
for filtering a zero level induced by the data modulation.
[0046] In other words, when the sequence of "one" and "zero" passes
through the filter (i.e. the ring resonator 4), each "one" level is
less attenuated than a "zero" level, which induces an increase of
the contrast between the two levels and therefore allows the zero
level to be filtered by the ring resonator 4.
[0047] This coupling is done via a waveguide 9 that is defined onto
the InP substrate 2 in a passive section, fed with photons by the
DML 3, and tangent to the ring resonator 4.
[0048] Preferably, this ring resonator 4 is butt-joined to the DML
3 in a passive material, in order to reduce insertion losses.
Indeed, the waveguide 9 and the ring resonator 4 must present the
lowest losses as possible to keep a high optical power. To do that,
they have to be designed in a passive material, which means a
material that doesn't absorb the optical power (typically with a
higher bandgap energy semiconductor).
[0049] It is important to note that the ring resonator 4 is only
used to filter the zero level induced by standard non-return to
zero modulation, by means of a resonance, in order to increase the
dynamic extinction ratio (or DER) rather than compensating the
fiber dispersion. The latter would require a too fine tuning of the
etalon and a complex feedback loop as in the CML third solution of
the art. The filtering operation of the ring resonator 4 is
tributary to the steepness of its characteristic slope, which is
preferably comprised between 1 GHz and 6 GHz, and if possible
between 1 GHz and 4 GHz, to be compatible with the adiabatic chirp
of the DML 3 and the fiber lengths in an optical access
network.
[0050] It is also important to notice that the DML 3 and the ring
resonator 4 operate together in close combination to optimize the
photon transmission.
[0051] The tuning means 5 is defined onto the InP substrate 2 and
arranged along the DML 3 and/or around the ring resonator 4 to tune
the photon wavelength and/or the ring resonator resonance used for
filtering.
[0052] The last sentence means that the tuning means 5 is either
arranged along the DML 3 to tune the photon wavelength while taking
into account the non-tunable filtering carried out by the ring
resonator 4, or arranged along the ring resonator 4 to tune the
filtering while taking into account the non-tunable wavelength of
the photons generated by the DML 3, or else arranged along the DML
3 and around the ring resonator 4 to tune not only the photon
wavelength but also the filtering. Using together the tuning means
is less attractive in terms of simplicity and cost reduction since
two different electrodes have to be used.
[0053] As illustrated in the non-limiting examples of FIGS. 1 and
2, the tuning means 5 may comprise heating electrodes arranged
along the DML 3 and/or around the ring resonator 4 and defining a
Peltier heater.
[0054] A thermally tuned ring resonator may comprise integrated
resistors, defined on top of it and defining the heating
electrodes, and a conductive layer defined above the integrated
resistors and intended for being fed with a current that is
arranged for inducing a thermal activity of its associated
integrated resistors. The resonance wavelength of the ring
resonator 4 is directly linked to the perimeter of the ring. As the
refractive index of the waveguide material changes with
temperature, the filtering (i.e. the resonance) can be adjusted by
free carrier injection using metal thin film resistors.
[0055] For instance, with a typical value of 100 .OMEGA. of a
resistive heating electrode 5, a power consumption typically equal
to 300 mW is required to shift the DML wavelength of 1 nm when the
heating electrode 5 is placed 20 .mu.m away from the DML 3. It is
possible, if the DML 3 is tuned, to increase the width and/or the
thickness of the resistive heating electrode 5 or to move it
further from the DML 3 to increase the current step for a
0.1.degree. C. shift or, if the ring resonator 4 is tuned, to heat
only a small angular section of it.
[0056] But in a variant not illustrated, the tuning means 5 may
comprise a controlled phase-shift section defined into the DML 3.
This phase shift section may be typically made of passive material
in which current is injected to create a carrier plasma which
results in an index change and consequently a wavelength
change.
[0057] The heating electrodes 5 as the phase-shift section
require(s) only few milliamperes to provide the requested tuning
(typically less than approximately 33 GHz for a 400 .mu.m radius
(of the ring resonator 4)). It is recalled that the wavelength
difference between ring resonator resonances is a function of the
ring perimeter (typically 33 GHz for 400 .mu.m radius). So, the
resonances being periodic, the maximum shift of the resonance or of
the laser wavelength is the free spectral range (i.e. the period of
the resonances) in order to recover the right laser
wavelength/resonance positioning.
[0058] One or more additional elements may be optionally added to
the emitting device 1 to optimize the optical eye reshaping for
data transmission.
[0059] For instance and as illustrated in FIG. 2, when a more
stringent control of performances is required, the emitting device
1 may further comprise a first semiconducting optical amplifier
(SOA) 6 defined inside the ring resonator 4 to modify the optical
losses. Its function is thereby to adjust the on/off ratio
characteristic and the steepness slope characteristic of the ring
resonator 4, to optimize the transmission. The on/off ratio
characteristic is the contrast value between the maximum of
transmission and the minimum down in each resonance of the transfer
function of the ring resonator 4.
[0060] This optional first SOA 6 can be advantageously defined
without extra technological step since the SOA material can be the
same as the one used for defining the DML 3.
[0061] It should be also noted that a passive taper section can be
also optionally defined in the emitting device 1 after the ring
resonator 4. Its function is to expand the optical mode guided in
order to reduce its divergence and improve the coupling with a
fiber for instance so as to reduce the insertion losses. It is
simply made by progressively reducing the width of the waveguide to
force the mode to move down and to expand.
[0062] Also for instance and as illustrated in FIG. 2, the emitting
device 1 may optionally comprise an integrated photodiode 7 defined
upward the DML 3 and arranged for monitoring optical power if
required. This optional rear photodiode 7 can be advantageously
defined without extra technological step since the photodiode
material can be the same as the one used for defining the DML
3.
[0063] Also for instance and as illustrated in FIG. 2, the emitting
device 1 may optionally comprise a second semiconducting optical
amplifier (or SOA) 8 defined downward the ring resonator 4 and
before the output, and arranged for compensating optical losses.
This optional second SOA 8 can be also advantageously defined
without extra technological step since the SOA material can be the
same as the one used for defining the DML 3.
[0064] When the emitting device 1 comprises a second SOA 8 and a
taper section, the latter is defined just after (or downward) the
second SOA 8.
[0065] The simple configuration of the emitting device 1 is of
great interest, notably for a production activity for which costly
screening steps have to be avoided. Indeed, the qualification of
components on a full wafer can be done only with the use of simple
measurements. For instance, the qualification of a single DML
requires evaluating the laser wavelength, the threshold current,
the optical power, the Side Mode Suppression Ratio (or SMSR)
through simple static characterizations, which can be easily
carried out with the emitting device 1. Indeed, the DML screening
can be measured at the output of the emitting device 1 or even at
the rear facet of the emitting device 1, the ring resonator
screening can be done through a simple tuning current evaluation
since the issue of laser wavelength stringent positioning can be
reduced to a power adjustment and thus an evaluation of a power
variation, the ring resonator peaks can be accurately identified by
a static power measurement and so does the tuning current by
recovering the variation of power previously evaluated in real
transmission experiments. In any case, the tuning current is
limited to a low value since the ring resonator response is
periodic (around 33 GHz for a 400 .mu.m radius). Therefore, the
laser wavelength variation over the full wafer (less than +/-0.1
nm) and the absolute position of the ring resonator peaks can
always be made up for by the tuning operation and the periodicity
of the resonance peaks of the ring resonator 4, which makes the
emitting device 1 tolerant to any variation of the effective
index.
[0066] For instance, the emitting device 1 may be produced by
implementing the process described below.
[0067] A first step of the process consists in an epitaxial growth
of the active structure of the DML 3 on the InP substrate 2. For
instance, MQW or quantum boxes are grown.
[0068] A second step of the process consists in carrying out a
butt-joint in order to allow growth of the passive structure. To
this effect one may first lay down a dielectric layer on top of the
active structure, and then one may implement a lithographic step to
define locations where holes, intended for receiving the passive
structure, must be defined. Then the active structure is etched,
for instance by reactive ion etching (or RIE) or inductively
coupled plasma (or ICP) or chemical etching, to define these holes,
and the passive structure is defined by epitaxy into the etched
holes. Finally the remaining part of the dielectric layer is
retrieved.
[0069] A third step of the process consists in defining, for
instance, a Bragg array into the active structure to define a DML 3
of the Distributed Feedback (DFB) type.
[0070] A fourth step of the process consists in defining active and
passive bands, and notably the waveguide with a ring shape, that is
part of the ring resonator 4, and the waveguide 9, coupling the DML
3 to the ring resonator 4 and tangent to the latter (4). Typical
distances between the waveguide and the ring resonator 4 are 100 nm
to 1000 nm.
[0071] A fifth step of the process consists, for instance, in
carrying out a p-doped re-growth both in the active and passive
sections. This requires a precise control of the re-growth
parameters to get an optimal growth morphology around the waveguide
part of the ring resonator 4 for specific critallographic
orientations.
[0072] A sixth step of the process consists in defining metallic
contacts for the DML 3.
[0073] A seventh step of the process consists, for instance, in
defining the metallic heating electrodes 5 near the ring resonator
4. This requires a precise calibration of the electrical resistance
of these metallic heating electrodes 5 to get the appropriate
heating of the ring for a given dissipated electrical power.
[0074] A eighth step of the process consists, for instance, in an
hydrogenation of the passive section for rendering the p doping of
the re-growth inactive. This requires a precise calibration of the
dosage, time and hydrogenation power, in order to limit absorption
losses of the optical mode inside the ring resonator 4.
[0075] In the emitting device 1 provided by the process described
above, the directly modulated laser 3 is an active structure being
epitaxially grown in an active section of the InP substrate while
the ring resonator 4 is a passive structure being defined in a
passive section of the InP substrate and being monolithically
integrated with said directly modulated laser 3.
[0076] This invention offers several advantages, amongst which:
[0077] a simple tuning means to facilitate the optimization of
transmission into an optical fibre and of an eventual screening for
a production phase, [0078] a reduction of the optical coupling
losses through full integration of a DML and a ring resonator (with
a butt-coupling or a silica PLC hybridization), [0079] no need to
use complex and power consuming electronic feedback loop, [0080] a
simple technological process with only two epitaxial growths,
[0081] it can be used for covering large distances (typically at
least 100 km) by optimizing the ring resonator steepness slope,
[0082] it can be used to compensate for chromatic dispersion by
exploiting the ring resonator negative dispersion in particular
around its critical coupling conditions, [0083] in the case of a
monolithical integration, a change of operation temperature would
affect similarly the effective index of the ring resonator and of
the laser, keeping the detuning between the laser wavelength and
the ring resonance constant. As such, it is expected to maintain
the optimized transmission performances even for un-cooled
operation.
[0084] It should be appreciated by those skilled in the art that
any block diagram herein represent conceptual views of illustrative
circuitry embodying the principles of the invention.
[0085] The description and drawings merely illustrate the
principles of the invention. It will thus be appreciated that those
skilled in the art will be able to devise various arrangements
that, although not explicitly described or shown herein, embody the
principles of the invention and are included within its spirit and
scope. Furthermore, all examples recited herein are principally
intended expressly to be only for pedagogical purposes to aid the
reader in understanding the principles of the invention and the
concepts contributed by the inventor(s) to furthering the art, and
are to be construed as being without limitation to such
specifically recited examples and conditions. Moreover, all
statements herein reciting principles, aspects, and embodiments of
the invention, as well as specific examples thereof, are intended
to encompass equivalents thereof.
* * * * *